Automatic frequency control system



Nov. 16,- 1948.

Filed Nov. 6, 1943 E. "r. JAYNES AUTOMATIC FREQUENCY CONTROL SYSTEM 3 Shasta-Sheet 1 v n 07/1/247/0 I {Z I! f L C/RCll/T f6 MIXER ai o/sckm/mrak 1 Z0041 TONI/V6 comma: MIC/14701? CIRCUIT /5 32 f7 INVENTOR T. JA YNES Nov. 16, 1948. E. T. JAYNES I 2,454,265

AUTOMATIC FREQUENCYCONTROLSYSTEM Filed Nov. 6, 1943 s Sheets-Sheet 2 i 7-0 srkur-n- ATI'ORNEY 7 Nov. 16, 1948. E. T. -JAYNES 2,454,255

AUTOMATIC FREQUENCY CONTROL SYSTEM Filed Nov. 1943 3 sheets sheet 5 70 STRUT g" E 94 fl/fl X m 9 95 ATTORNEY Patented Nov. 16 1948 AUTOMATIC FREQUENCY CONTROL SYSTEM Edwin T. Jaynes, Garden City, N. Y., assignor to The Sperry Corporation, a corporation of Dela.-

ware

Application November 6, 1943, Serial No. 509,262

19 Claims.

The present invention relates to the art including automatic frequency control systems, especially for ultra high frequency oscillators of the thermally-tuned Klystron type. In such oscillators la frequency-determining element in the form of a cavity resonator is tuned to determine the output frequency. The resonator tuning means comprises a thermally expansible strut or element which varies the resonator tuning upon expansion or contraction thereof. This expansion is caused by the application of electrical power to the strut, either by electrical conduction through the strut or by application to a heating coil in close contact with the strut.

The present invention is more particularly directed toward improved circuits and apparatus for controlling the application of this electrical power to effect the expansion of the tuning strut. For this purpos corresponding deviation of the output frequency of the resonator from a desired Value. This control signal. then controls the application of electric power to the thermal tuning control element or strut to restore the oscillator to its desired frequency value by returning one or'more resonators thereof.

Such electrical power is preferably of the altermating type in order to gain ease of control and amplification and to produce a minimum of undesired interaction between the applied power and the electron beam of the oscillator, due to the inherent magnetic fields associated with such electric power. For this reason the power frequency utilized is preferably of'a value higher than any modulation frequency which it is desired to apply to the oscillator or which is utilized in the system, and also sufficiently high so that the inherent thermal inertia of the expansible tuning control, element will prevent any fluctuation in the extension of this control member in response to the alternation of the applied power.

Accordingly, it is an object of the present invention to provide improved frequency control apparatus for ultra high frequency oscillators, especially but not necessarily of the thermally tuned type.

It is another object of the present invention to provide an improved automatic frequency control system for thermally tuned ultra high frequency oscillators by controlling the application of electrical power to the thermal tuning element of such oscillators. It is a further object of the present invention 'to provide improved apparatus for controlling the a control signal is produced mally-responsive tuning element in an ultra high frequency oscillator to control the frequency thereof.

It is another object of the present invention to maintain an ultra high frequency thermally tuned oscillator in a desired frequency condition by control of the application of alternating electrical power to the thermal tuning control element of this oscillator.

ther objects and advantages of the present invention will become apparent from the specification and drawings, wherein Fig. 1 shows a schematic block diagram of a system in which the presentinvention may be utilized; i

Fig. 2 shows a schematic wiring diagram of a portion of the system ofFig. 1 and incorporating certain features of the present invention;

Fig. 3 shows a schematic wiring diagram equivalent to a portion of the circuit of Fig. 2;

Fig.4 shows a schematic wiringdiagram similar to the circuit of Fig. 2;

Fig. 5 shows a schematic wiring diagram also similar to the circuit of Fig. 2;

Fig. 6 shows a schematic wiring diagram of a circuit having certain advantages over that of Fig. 2; v

Fig. 7 shows a. schematic wiring diagram similar to the circuit of Fig. 6;

Fig. 8 shows a schematic wiring diagram of a modified form of the invention;

. Fig. 9 shows a schematic wiring diagram of an improved form of the present invention;

Figs. 10 and 11 show schematic wiring diagrams of portions of a circuit useful in the system of Fig. 9.

Referring to Fig. 1, there is shown one form of system in which the present system may be utilized. This figure illustrates a superheterodyne receiving system in which a received wave excites a receiving antenna ll connected to a mixer 12.

A-local oscillator l3 supplies its output wave to the mixer l2, which thereupon produces a difierence or intermediate frequency having the same modulation as the wave received by antenna ll.

This intermediate frequency is amplified by a suitable amplifier l4 whose output is connected to any desired type of utilization circuit 15. Amplifier l 4 is generally of the tuned type to provide suitable selectivity for the received wave, and, accordingly, it is desirable to maintain the output frequency of oscillator l3 in fixed relation to the frequency of the wave received by antenna H and differing therefrom by an amount equal to the tuned intermediate frequency of amplifier criminator It then actuates a tuning control circuit ll, which is adapted to readjust the output frequency of oscillator It to the value producing the desired intermediate frequency.

It will be understood that in place of the receiving antenna ll, there may be connected any suitable source of reference frequency with respect to which it is desired to maintain the output frequency of oscillator i3 in predetermined frequency relation, such as having fixed frequency difference with regard thereto. Alternatively, oscillator l3 may be connected directly to a suitable ultra-high-frequeney discriminator functionally equivalent to discriminator l5.

Fig. 2 shows one form of discriminator it in association with a tuning control circuit I? according to the present invention, for controlling an oscillator i3. Oscillator I3 is shown as being of the thermally tuned Reflex Klystron type,

although it may be of any high frequency type,

preferably thermally tuned. Reflex Klystron oscillators are illustrated in Fig. 2 of Varian and Hansen Patent No. 2,250,511, issued July 29, 1941, and carry R. M. A. designations such as 21137, 2K39, and 21121.

Oscillator I3 is illustrated as comprising a grounded resonator having a pair of electronpermeable grids defining a gap 22 through which an electron 'beam from a cathode 23 is projected by means of a battery 24 connected between cathode 23 and the grounded resonator 2|. The electron beam passing through resonator 2| is reversed and reflected by a reflector electrode 25 which is maintained at a suitable slight voltage difference with respect to cathode 23 by means of its connection to a variable tap 26 on battery 2 The output frequency of oscillator l3 may be controlled or adjusted by adjusting the resonant frequency of resonator 2 i This may be done by distorting one wall of the resonator 2!, which may be made flexible for this purpose, as shown at 20,

Such adjustment may be so as to adjust gap 22. effected by means of a tuning control strut member schematically illustrated at 21, whose expansion and contraction is controlled by electric power supplied thereto. In'the present instance, such electric power is illustrated as applied to the center of strut 21|by means of a connection 28, the ends of strut 21 being grounded by means of their abutting connection to flanges on resonator 21. In this way electric current may be made to fiow in the two halves of strut 21. Such current flow produces internal heating of the strut, which thereupon expands and varies the spacing of resonator 2|. This expansion may be opposed by means of suitable springs (not shown) and atmospheric pressure on the evacuated resonator,

which serve to return the resonator to its' toward the provision of improved control circuits for controlling the energization of strut 21. In

4 order to derive a control signal for controlling the strut excitation, the output of intermediate frequency amplifier i4 is supplied to a discriminator l6 of conventional type which is adapted to produce an output control voltage between its output lead 3! and grounded lead 35 of a magnitude proportional to the magnitude of the frequency deviation of theintermediate frequency from the value to which the discriminator I6 is tuned, this output voltage having a polarity corresponding to the sense of this frequency deviation. That is, for intermediate frequencies below the desired value, a positive output voltage is derived from discriminator It; for intermediate frequencies above the desired value, a negative output voltage is produced.

According to' the present invention, this discriminator output control signal controls the application of alternating power from a source 32 to the strut 27. Source 32 is connected to a transformer 33 having a voltage divider 3 connected across the secondary thereof. The mova'ble tap 35 of the voltage divider 34 is grounded. One end, illustrated as the left end'in Fig. 2, of the transformer secondary is connected through a blocking condenser 35 and a load resistor 31 to the anode of a control tube 33. The grid of control tube 38 is connected directly to output lead SI of discriminator [5. The cathode of the tube 38 is connected to ground through a biasing resistor 39 having a by-pass condenser 4!. The anode of tube 38 is connected through the resistor 37 and a further resistor 52 to a source 43 of positive anode voltage. Source 43 may be bypassed to ground through a by-pass condenser 44' so as to maintain substantially constant unidirectional potential. The anode of tube 38 is connected through a coupling and blocking condenser 45 and a grid input resistor E5 to the control grid of a power amplifier tube 47. The second end of the secondary winding of transformer 33 is also connected to the'grid of amplifier 4"! through a blocking condenser 48. It will be seen that condensers 36 and 4 8 prevent the grounding of the anode of tube 38 or the grid'of amplifier 41 by virtue of the ground connection of tap 35 of voltage divider 34.

Tube 38 acts effectively as a variable resistance under the control of the voltage applied to its grid by lead 3!. The equivalent circuit of this tube is shown in Fig. 3, where the variable resistance 38 represents the resistance of the tube 38. This variable resistance 38 is connected in series with the resistance 31' across source 32' which represents the voltage developed across that portion of resistor 34- between the left end of the secondary winding of transformer 33 and the grounded variable tap 35. In this way the alternating potential of point 40, corresponding to the anode potential of tube 38, may be varied by variation in the, resistance 38 under the control of the discriminator output voltage.

This alternating potential is combined with a second alternating potential derived from source 32 which represents the voltage developed across that portion of resistor 34 between the grounded tap 35 and the right end of the secondary of the transformer 33 of Fig. 2. As is indicated in Fig. 3, the alternating voltage of source 32 is connected in phase opposition to that of source 32". The reason for this may be seenirom the following considerations. The actual variation in resistance of tube 38 under the control of the discriminator output voltage is relatively small,

producing only a'small variation in the alternating potential of point 48. For example, the potential at point 40 may vary between 100 and 110 volts. The proportional orpercentage variation of this alternating potential may be increased by subtracting a fixed amount from this variable voltage. For example, if the source 32" has a voltage of 90 volts, the resultant voltage applied to the input of tube 41 of Fig. 1 will vary be--' tween 10 and 20 volts, representing a much greater proportional change. Also, in this way, the average voltage obtained is lowered to a more suitable value, which, as will be seen, determines the normal oscillator frequency. The diiference between the variable voltage derived from source 32' and the fixed voltage derived from the source 32" is amplified in the power amplifier 47, whose output is coupled to the tuning strut 21 by a suitable power transformer 49, and thereby serves to correspondingly control the tuning of oscillator l3.

In operation, with zero output from discriminator It, the variable tap 35 is adjusted to a point such that the alternating power applied to strut 21 is of the proper value to produce an oscillator output frequency which differs from the received wave or reference frequency by the desired intermediate frequency. Thereafter, any variation in the relation between the reference frequency and the oscillator frequency will produce a corresponding signal output from discriminator l3. This output signal will correspondingly increase or decrease the effective resistance of tube 38 so that the alternating voltage applied to amplifier 41 will correspondingly increase or decrease, providing a corresponding change in the power applied to the tuning strut and returning the oscillator to provide a new oscillator frequency which has the desired relation to the reference frequency. In this manner the frequency of oscillator I3 is maintained in substantially fixed relation to the reference frequency supplied to the mixer I2. Variable tap 35 will therefore be seen to provide means for setting the datum of the system which will be maintained by the control action of the control circuit utilized.

Fig. 4 shows a system similar to Fig. 2 in which a slightly different connection for the source 32 is utilized. In this figure the positive potential source 43 is connected to the variable tap 35 of the voltage divider 34 connected across the seconclaryof the transformer 33 energized from source 32. The by-pass condenser 44 eifectively grounds tap 35 with respect to alternating potentials, so that the circuit of Fig. 4 operates in the same manner as that of Fig. 2. Blocking condenser 48 now serves to isolate the grid of tube 4'! from the high positive potential of source 43. The blocking condenser 36 and the isolating resistor 42 of Fig. 2 are no longer necessary.

In Fig. 5 the variable resistance provided by tube 38 is connected in series with an adjustable resistance in the cathode circuit of tube 38. Thus, a variable resistor 5| is provided connected between a positive source (which may be the same as source 43) and the cathode of tube 38, which is connected to ground by an adjustable resistor 52 having anadjustable tap 53. In this manner the resistor 52 is in series with the variable resistance provided by tube 38. Thediscriminator output is connected between the grid of tube 38 and, ground, as by terminals 54. Source 32 now energizes, the. circuit by the conmotion ofthe secondary of transformer 33 in series between the anode of tube 38 and positive source 43. By-pass condenser 44 again serves to connect the secondary of transformer 33 to ground. i

It will be seen that with a zero signal applied to the grid of tube 38 from the discriminator, the bias provided by the action of resistors 5| and 52 serving as a voltage divider will cause a predetermined alternating voltage to appear across resistor 52, through the action of tube 38 as a cathode follower device. This voltage may be adjusted by suitable adjustment of tap 53 and is then utilized to energize the tuning strut in the manner to be described below, to provide the normal and desired oscillator frequency. Upon the appearance of a signal from the discriminator, the bias on the grid of tube 38 is correspondingly changed, producing a change in its plate resistance and a corresponding change in the alternating voltage component appearing across resistor 52. The relationship between the distributor signal impressed on the grid of tube 38 and the resulting change in alternating voltage produced can be adjusted by adjusting the resistance 5| to adjust the bias acting on grid 38.

To utilize this voltage component to control the tuning strut, the primary of a voltage transformer 55 is connected to the cathode of tube 33 through a blocking condenser 58 and is also connected at its other terminal to ground. In this way the alternating component of voltage across resistor 52 is impressed across the primary of transformer 55, while any direct current fiow is blocked by condenser .56. The secondary of transformer 55 is center-tapped and is connected to a push-pull power amplifier stage comprising tubes 41' and 41" which have the same function as the power tube 41 of the prior circuits. The output of amplifier 41', 41" is connected to the tuning strut through a power transformer 49. This circuit thus operates in similar fashion to the prior-described circuits.

Fig. 6 shows a. further refinement on the circuit of Fig. 5. Thus, the control tube is shown as a double triode 38'. The first section of this double triode 38, comprising anode 56, grid 51 and cathode 58, is connected in a manner similar to tube 38 in Fig. 5; that is, the secondary of transformer 33 which is energized from source 32 is connected between positive source 43 and anode 53. Source 43 is also by-passed to ground by condenser 44. Cathode 58 is again connected to a voltage divider 5|, 52 which serves to provide bias for the grid 57 and as a cathode follower resistor. One of the input terminals 54 is connected to grid 5! through a resistor 59. A condenser 6| is connected between grid 51 and cathode 58. The other of input terminals 54 is supplied with a suitable potential from a second voltage divider 6|] which may also be energized from source 43 or any other source of positive unidirectional potential.

This first section of tube 38 operates in essentially the same manner as does Fig. 5. The voltage divider merely permits the bias on grid 51 to be set independently of the adjustment of resistor 5| forming part of the voltage divider 5|, 52. In this way a voltage is developed across adjustable resistor 52 in the same manner in Fig. 5. i Resistor 59 and condenser 5| serve to filter out any transient pulses which may appear in this discriminator output and supply a slight amount of delay in the response of the control circuit to the output signal so that operation of the control circuit is smoothed. I

The second section'of the double tube 38, "comprising anode 62, control grid 63, and cathode fi l, serves as an amplifier for the voltage-appearing across resistor 52. Thus, it will be clear that this voltage is also impressed between grid 63 and cathode 6d, and therefore will be amplified by the second section of tube 38'. The operating bias of grid 63 may be independently adjusted by the adjustable tap 65 on voltage divider 60. The output of this second section then energizes the input transformer 55 for the pushpull amplifier cl, 4'!" and thereby energizes the tuning strut 2'! of the oscillator l3.

Fig. '7 shows a circuit similar to that of Fig. 6, in which a greatly increased amplification may be obtained. In the circuit of Fig. 7 the grid 63 of the second section of double triode 38' isconnected directly to grid 51 instead of having a fixed bias. Thus, when, for example, the discriminator output becomes positive, producing a decreased resistance for the first section of tube 38 and increasing the voltage across resistor 52,

this same positive potential is applied to grid 63, further increasing its amplification of the voltage across resistor 52. In this way much higher amplifications of the strut controlling voltage are obtained for large frequency deviations, permitting the circuit to operate more A quickly to restore the oscillator frequency to its proper value when the relationship between oscillator and reference frequencies has changed. The amplified output of the second section of tube 38 is supplied to thetransformer 55 and the push-pull amplifier ll, M" to energize the tuning strut. v

It will be clear that in Figs. 5, 6 or '7 a single power amplifier such as 41 of Figs. 2 or 4 may be utilized, and, conversely, a push-pull amplifier of the type shown in Figs. 5, 6 or '7 may be utilized in Fig. 2 or 4.

Each of the preceding circuits has derived the alternating strut energizing voltage through what is essentially Variable voltage divider action. In Fig. 8, however, the discriminator output is utilized to modify the amplification of an alternating voltage and thus provide a variable alternating voltage for use in energizing the strut. I

In Fig. 8 the discriminator output is impressed on a control grid H of a double triode 12 similar to tube 38'. The anode 13 of tube 12 is connected directly to the positive source 43. Cathode 15 is connected to ground through a cathode follower resistance 15 by-passed by condenser 16. The grid ll of the second section of tube 14 is energized by an alternating voltage from source 32 which is made adjustable by voltage divider l8. Cathode I9 is connected to cathode l4, and anode 8! is connected through the primary of transformer 55 to the positive voltage source 43. Transformer 55 then energizes the power amplifier feeding the tuning strut.

In operation, assuming for the moment z'ero discriminator output, the normal or zero-input current passing through the first section of tube 12 produces a predetermined voltage across resistor 15 which provides the bias for grid TI. This voltage and the alternating voltage impressed on grid l! are adjusted to provide the excitation for the tuning strut necessary for the desired normal operating frequency of oscillator [3.

A positive potential derived from the dlscrimi natorahd impressed on the grid M will increase the drop across resistor 15 and will thereby decrease the excitation of the tuning strut. Corre'spondingly, a negative output from the discriminator will decrease the voltage across resistor l5 and will increase the amplification of the alternating voltage impressed on grid Tl, thereby producing greater tuning strut excitation. By a proper choice of the po ty o the discriminator output relative to the desired change in oscillator voltage, this action will serve to maintain the oscillator frequency at the desired value. Voltage divider '58 may be adjusted and provides a manual tuning control for the oscillator frequency just as in the preceding figures.

Fig. 9 shows a more complete circuit diagram for the present invention operating in a fashion similar to that of Fig. 8. In this figure, source 32 and transformer 3-3 are connected to a bridge network, comprising a voltage divider 8! having a grounded adjustable tap 82, and a pair of equal resistances 83, 84. Resistor 83 may be provided with an adjustable tap 85 connected to the grid of power amplifier 86 similar to tube 41 of the prior circuits. Blocking condensers 81 and 89 are inserted in the circuit for direct current isolation but have no effect upon the alternating current bridge. By proper adjustment of the tap 82, zero alternating voltage will appear between the junction 91 of resistors 83, 8t and ground. Junction 9! is then supplied with a unidirectional voltage which provides the bias for tube 86 and controls the amplification of the alternating voltage impressed upon the grid of tube 86 by means of tap 85. Junction 9! is connected through an isolating resistor 92 to a single-pole, double throw switch 93, which is adapted to render the automatic frequency control system operative or inoperative. i

In the on position of switch 93, a potential is impressed at junction 9| whichis controlled by the discriminator I6. As shown in Fig. 9, one terminal 3| of discriminator i6 is connected directly to switch 93. The other terminal 30 of discriminator i5 is connected through a resistor 94 to a source of negative potential 95. A by-pass condenser 96 is connected between this latter terminal so and ground to by-pass all alternating current components. Alsoconnected to this terminal 3!] is the cathode 9'! of a control tube 98 whose anode 99 is grounded. The grid IUI of control tube 98 is connected to the junction I02 of a resistor I03 and condenser lMconnected between the two terminals 30 and 3| of discriminator 16, a suitable battery or other bias source we being interposed in the circuit of grid llll.

In operation, and momentarily assuming zero outputfrom discriminator I6, tube 98 and resistor 94 are so selected and arranged that the potential of lead 30 provides a desired normal bias voltage for tube 86. This bias is just beyond cuton, so that adjustment of tap 85 will permit tube 86 to conduct only during less than one-half cycle of source 32. By properly setting tap 85, the oscillator frequency may be adjusted to its normal value, or be manually tuned. The appearance of a positive or negative discriminator output voltage correspondingly modifies this bias and thereby changes the amplification of tube 86 to vary the energization of the tuning strut and to vary the oscillator frequency to maintain its desired condition.

The present circuithowever, also provides an additional feature which shifts the normal bias for grid 86 in response to -a persisting off-fro quency condition of the oscillator I3. Such apersisting off-frequency condition is evidenced by a fixed voltage output from discriminator I6. Such a fixed voltage output will charge up condenser I84 and will thus vary the potential of grid IDI. This, in turn, varies the current passing through resistor 94 and correspondingly changes the potential of lead 30 which determines the normal bias for tube 86. Resistor I 83 and condenser me have a sufficiently long time constant so that tube 98 does not respond to rapid or short changes in discriminator output. In this way a persisting tendency to change frequency is substantially overcome, and the oscillator frequency is maintained more nearly constant at its desired value. With switch 93 turned to the off position, voltage divider I01 energized from source 95impresses normal bias on tube 86 and thereby provides the same operating condition, but adapted only for manual control by means of tap 85. a Fig. 10 is similar to Fig. 9 and shows only the portion of Fig. 9 Within the dotted rectangle I08. In Fig. 10 the bias for the grid I of tube 98 is provided by a resistor I89 connected in series with its cathode 91. No by-pass condenser is needed for resistor I09, since tube 98 responds exclusively to unidirectional potentials. Otherwise Fig. 10 is the same as the corresponding part of Fig. 9. I

Fig. 11 shows another similar circuit, again being similar to the portion in rectangle I88 of Fig. 9. In Fig. 11, however, the adjustment of the normal bias for tube 86 is provided by selecting resistor 94 and condenser 96 to have a large time constant so that any transient or shortduration signals impressed on grid IOI will be able to change the potential of lead 38 only after condenser 96 has become charged. With a long time constant circuit 94, 96, therefore, the change in the potential of lead 30 will correspond only to persisting signals impressed on grid IUI, and the circuit will therefore function in the same manner as the circuits of Figs. 9 and 10.

Fig. 11 also includes a provision for rendering the automatic normal bias adjustment of tube 88 inoperative. For this purposea voltage divider MI is connected between source 95 and ground. The tap IIZ of voltage divider III is chosen to provide a potential equal to the normal bias desired for tube 86. By making the resistance of voltage divider III small in comparison to the series circuit composed of resistor 94 and tube $8, and by closin switch H3, the potential of lead 36 is determined almost exclusively by voltage divider III and is rendered substantially independent of any control by tube 98. Thus, upon closing switch H3, the effect of tube 98 is almost eliminated, and the circuit will operate in a fashion similar to that of Fig. 8.

It will be apparent that in each of the circuits herein described, the output of the discriminator may also be supplied to a suitable utilization circuit I which will thereby respond to a demodulated version of any frequency modulated signal received by antenna II.

Accordingly, by the present invention I have provided an extremely useful and highly efficient automatic frequency control system particularly adapted to the automatic frequency control of thermally tuned high frequency oscillators.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made Without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not I quency-determining circuit and thermally-actuated means for tuning said circuit, means for-deriving a control signal corresponding to deviation of the output frequency of said oscillator from a desired value, a control tube having an anode, a 7 control grid and cathode, means connecting said signal-deriving means to said control grid to impress said control signal thereon, an output impedance, a source of alternating voltage, means connecting said source between said anode and cathode in series with said output impedance, means for deriving an alternating output voltage from said output impedance, a source of adju'stable alternating voltage, means for combining said alternating output voltage in phase opposition with an adjustable alternating voltage derived from said latter source, and means for heating said tuning means by said combined voltages to restore said oscillator frequency to the desired value.

2. The apparatus defined in claim 1, wherein said ouput impedance is connected in the plate circuit of said control tube.

3. The apparatus defined in claim 1, wherein said output impedance is connected in the oathode circuit of said control tube, said control tube being adapted to operate as a cathode follower.

4. Automatic frequency control apparatus for a variable-frequency device having a frequencydetermining element and means for tuning said element, ='said apparatus comprising means for deriving a control signal whose magnitude corresponds to the magnitude of the deviation of the frequency of said device from a desired value and whose polarity corresponds to the sense of said deviation, a multi element control tube, means connecting said signal-deriving means to one of the elements of said tube, anoutput impedance, a source of alternating voltage connected to said control tube in series with said output impedance, means for deriving an alternating output voltage from said output impedance,

a second source of alternating voltage, means combining said alternating output voltage in phase opposition with an alternating voltage derived from said last-named source, and means .for actuating said tuningmeans in accordance 'ated means for tuning said circuit, means for producing a control signal corresponding to deviation of the ouput frequency of said oscillator from a desired value, a control tube having a control grid and an anode, means for connecting said signal-deriving means to said control grid to im press said control signal thereon, a source of alternating voltage, means for connecting said source of alternating voltage to said anode,

a source of adjustable alternating voltage, I means for combining the alternating output voltage of said tube with, said adjustable alternating voltage in phase opposition thereto, and means for controlling said thermally-operated tuning means by said combined voltage to maintain said o c llator output frequency at the desired value.

F eq e cy con r appa tu c p i n a controlled oscillator, means for producing a signal whose magnitude corresponds to the mag: nitude of the deviation of the output frequency of said oscillator from a desired value and whose polarity corresp nds to the sense Of said deviation, a control tube having a control grid and an anode, means for impressing an alternating voltage on said anode, means for controlling said control grid by said signal, means for combining the output ofsaid control tube with a fixed alternating voltage in phase opposition to said first voltage, and means for controlling the frequencyof said oscillator by. said combined voltages.

7. Frequency control apparatus, comprising a controlled frequency source, means for producing a signal whose magnitude corresponds to the magnitude of the deviation of the output frequency ofsaid source from a desired value and whose polarity corresponds to the sense of said deviation, 3, variable voltage divider, a source of alternating voltage connected across said divider, means coupled to said signal-producing means and tosaid divider. for controlling the ouput alternating voltage ofsaid divider by said signal, and means for controlling the frequency of said source by said output alternating voltage.

8. Automatic, frequency control, apparatus, comprising a controlled oscillator having a there mally tuned frequenoyedetermining circuit, means for deriving a control signal corresponding to deviation ofthe output frequency of said oscillator from a desired value. a pair of control devices, eachhaving an anode, cathode and grid,

said cathodes being. connected together and said grids. being connected together, a common resistor me n onne ted o s id ca h des, means. for connecting said signal-deriving means to, said, grids to impress said control signal thereon, a source of; alternating potential connectedtoone of said anodes, and means. for tuning, said circuit in response to the, alternating component of the current flowing to said, other. anode to restore, said oscillator. frequencyto its desired value.

9,. Automa ic freq ency contr l pparatus. comprising. a controlledfrequency, source having a frequency-determining. circuit, means for producing a control signal whose magnitude corresponds to the magnitude of the, deviations of e. ut t requ cy sa d source. from a desired value andvvhose polaritycorresponds tothe sense ofsaid deviation, means. responsive to said control signal for deriving an alternating voltage corresponding to, said signal, means for; amplifying said alternating voltage, means for controlling said amplifying means in response to, said control signal, and means. responsive, to. said amplified; voltage for tuning, said circuit to. restore said source frequency to and maintain it at d: de i ed va ue.

1Q. A frequency control apparatus, comprising a controlled oscillator having a thermally-tuned frequency-determining. circuit, a source'of adjustable alternating potential, means for controlling said circuit. by said potential whereby the output frequency. of. saidoscillator may be adjusted to a desired. value by adjustment of said potential, an amplifier device connected between said source and said circuit, means for modifying the amplification 'rfsaid "devicain accorda ce maintainer 9i e. .x i t requ r m l! deemed.- Va ue to re t re Sa Q'bSci la rIf que v to ts, es ed ame. nd mass! re p r. ee per isti des gner i t n can oscillator frequency for modifying said adjusted potential.

11, Apparatus as in claim 10, wherein said lastnamed means comprises an electron discharge device whose conductance is delayedly controlled in response to said deviations.

12, Frequency control apparatus, comprising a controlledpscillator having an adjustable frequencyfdetermining circuit, a source of adjustable alternating potential, means for adjusting the frequency of said circuit in response to said potential, said adjusting means comprising a variable amplification device having a normal amplification, means responsive to frequency deviation of said controlled oscillator frequency from a desired value for modifying the amplification of said device with respect to said normal amplification so as to restore said oscillator frequency to its desired value, and further means responsive to persisting oscillator frequency deviations for modifying said normal amplification.

13. Automatic frequency control apparatus, comprising a controlled oscillator having an adjustable frequency-determining circuit, a source of adjustable alternating potential, means for adjusting the frequency of said circuit in response to said potential, said adjusting means comprising an amplifier having variable amplification'and a normal bias, means for producing a control signal responsive to frequency deviation of said controlled oscillator frequency from a desired value, means for superposing said signal upon the normal bias of said amplifier to modify the amplification thereof so as to restore said oscillator frequency to its desired value, and furthermeans. responsive to persisting oscillator frequency deviations for modifying said normal bias.

14. Frequency control apparatus, comprising a controlled oscillator having an adjustable frequency-determining circuit, means for adjusting the frequency of said circuit and comprising a variable amplification device having a normal amplification, means responsive to frequency deviation of said controlled oscillator from a, desired value for modifying the amplification of the; device to restoresaid oscillator frequency to its desired value, and further means responsive t0 persisting oscillator frequency deviations for modifying said normal amplification.

1 5 Frequency control apparatus, comprising a controlled frequency. source having an adjustable, frequency-determining circuit, means for adjusting the frequency of said circuit in response to frequency deviation of said controlled source frequency from a desired value, said adjusting. means including an amplifier having a variable amplification and a, normal bias, and means responsive to persisting source frequency deviations for modifying said normal bias.

16. Frequency control apparatus, comprising a controlled frequency source having an adjustable, frequency-determining circuit, means responsive to deviation of said controlled source frequency from a desired value for restoring said source frequency to its desired value, and further means responsive to persisting source frequenci deviations for modifying the control action of said restoring means whereby said source may be kept in closer correspondence to its desired value.

17. Frequency control apparatus for a variablefrequency device comprising means for producingrasignal whose. magnitude corresponds to the.

magnitude of the deviation of the frequency of said device from a desired value and Whose polarity corresponds to the sense of said deviation, variable voltage-dividing means, a source of alternating voltage connected across said voltagedividing means, means coupled to said signal producing means and to said voltage-dividing means for controlling the alternating voltage output of said voltage-dividing means in response to said signal, and means for controlling the frequency of said device by said alternating voltage output.

18. Frequency controlling apparatus for a high frequency device having an adjustable frequencydetermining element, said apparatus comprising means for adjusting the frequency of said element in response to frequency deviation of said device from a desired value, said adjusting means including an amplifier having a variable amplification and a normal bias, and means responsive to persisting device-frequency deviations for modifying said normal bias.

19. Frequency control apparatus for a high frequency device having an adjustable frequencydetermining element, comprising means responsive to deviation of said device-frequency from a desired value for restoring said device-frequency to its desired value, and further means responsive to persisting device-frequency deviations for modifying the action of said restoring means whereby said device-frequency may be kept in close correspondence to its desired value.

EDWIN T. JAYNES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,041,855 Ohl May 26, 1936 2,151,127 Logan Mar. 21, 1939 2,283,523 White May 19, 1942 FOREIGN PATENTS Number Country Date 537,518 Great Britain June 25, 1941 Certificate of Correction atent No. 2,454,265. November 16, 1948.

EDWIN T. J AYNES It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 23, for the word distributor read discriminator; column 10, line 62, claim 5, for ouput read output;

and that the said Letters Patent should be read with these corrections therein that the ame may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 14th day of June, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

